LONDON (Reuters) – Queen Elizabeth, the world’s oldest and longest-reigning monarch, celebrated her 91st birthday in a usual low-key fashion on Friday.

Artillery gun salutes in London’s Hyde Park and at the Tower of London will mark the occasion although the queen, who normally spends her birthday privately, has no formal engagements planned herself.

Elizabeth was born on April 21, 1926 in Bruton Street in central London when Calvin Coolidge was U.S. President and Joseph Stalin had just taken control in the Soviet Union and became queen in 1952 at 25.

Despite her age, she still regularly carries out official duties although she has cut back on the number of engagements in recent years, passing these onto other members of the Windsor family such as to her son and heir Prince Charles and grandsons, Princes William and Harry.

Polls show she remains very popular amongst Britons and royal aides say there is little prospect of her abdicating. Asked if she was well during a trip to Northern Ireland last year, she quipped “Well, I’m still alive”.

The queen has an official birthday in June which is publicly marked with a large parade of soldiers through central London, known as Trooping the Colour.

Britain’s Queen Elizabeth leaves after a visit to Priory View, an independent living scheme for older residents, in Dunstable, Britain April 11, 2017. REUTERS/Peter NichollsMembers of the royal family, including Catherine, Duchess of Cambridge holding Princess Charlotte, Prince George, Prince William, Queen Elizabeth, and Prince Philip stand on the balcony of Buckingham Palace after the annual Trooping the Colour ceremony on Horseguards Parade in central London, Britain June 11, 2016. REUTERS/Toby MelvilleBritain’s Queen Elizabeth in London in this February 29, 2012 file photo. REUTERS/Eddie Mulholland/Pool/FilesMembers of the Royal Gibraltar Regiment hold onto their caps in the wind as they prepare to fire a 21 gun salute to mark the 91st birthday of Britain’s Queen Elizabeth in the British overseas territory of Gibraltar, historically claimed by Spain, April 21, 2017. REUTERS/Phil NobleMembers of the Royal Gibraltar Regiment fire a 21 gun salute to mark the 91st birthday of Britain’s Queen Elizabeth in the British overseas territory of Gibraltar, historically claimed by Spain, April 21, 2017. REUTERS/Phil NobleMembers of the Royal Gibraltar Regiment fire a 21 gun salute to mark the 91st birthday of Britain’s Queen Elizabeth in the British overseas territory of Gibraltar, historically claimed by Spain, April 21, 2017. REUTERS/Phil NobleGuns are fired during the King’s Troop Royal Horse Artillery Royal 41-gun salute to mark the 91st birthday of Britain’s Queen Elizabeth, at Hyde Park in central London, Britain April 21, 2017. REUTERS/Stefan WermuthQueen